Doesn't the method shown (below) offer considerable difficulties if, say, a third bit of vendor software adds itself to the pile using the same technique? If you don't think so, then imagine what will happen when vendor #2 trips its abend routine and decides to back itself out. The BEST it can manage would be to return the environment to the state it found it in... which won't do vendor #3 any good at all (actually it will cause vendor #3 some harm, as well as the customer) and it might even mess up vendor #1. Consider that vendor #1 might have code that would otherwise make dynamic changes to its SVC screening table -- except that vendor #2 has supplanted it so #1's table isn't hooked to anything anymore.
There ought to be a better way... On Tue, 4 Apr 2006 15:34:54 -0700, Ray Mullins wrote: >If you mean the old >save-the-current-address-and-stick-my-address-in-the-table-and-then-pass- >control-to-the-old-routine-when-I'm-done-with-it method... > >A product that utilizes SVC screening should check to see if screening is >already in place, i.e., the existence of a screening table in the TCB. It >should then save the address of the already existing routine somewhere in >its storage, store its address in the screening area, save the current >table, and flip on the bits for the SVC that it wants to screen - and not >flip off any bits. Then, if its code gets control for an SVC that it isn't >expecting, it knows that there is another screening routine that might want >it, so it should pass it on to the routine whose address it saved at >initialization. And for SVCs that the new routine does screen, when it's >done it should then check the old SVC screening table to see if the prior >SVC routine wants it. > >> -----Original Message----- >> Subject: SVC Screening -- again >> >> I searched the archives for SVC screening posts and saw quite >> a few postings regarding when to use it and what to use it >> for. What I am looking for (and didn't find in the archives) >> is how multiple screening programs are implemented. For >> example, what if products from different vendors want to do >> SVC screening on the same TCB? Is there a de facto method >> that vendors use similar to the one used for front-ending SVC's? -- Tom Schmidt Madison, WI ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
